A mixture of mycolylacetyltrehalose from Mycobacterium tuberculosis and endotoxin preparation from the Re mutant of Salmonella typhimurium in oil droplets has a potent antitumor activity when tested against transplanted hepatomas in syngeneic guinea pigs. The endotoxin preparation has now been shown to contain trace amounts of an unknown component that is required along with the purified endotoxin for the tumor regression activity. Results suggest that this factor could be a peptide-containing lipid. Purification and characterization of this factor is in progress. We have now developed a suitable murine tumor assay system to test immuno-therapeutic agents. CDF1 mice and P-388 tumor cells are used in this assay. We are now studying the effects of the glycolipid-endotoxin mixture on this assay system.